1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method for performing a bandwidth request procedure.
2. Description of the Related Art
An IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard provides techniques and protocols to support a broadband wireless access. Its standardization started in 1999 and IEEE 802.16-2001 was approved in 2001. The IEEE 802.16 standard is based on a single carrier physical layer called ‘WirelessMAN-SC’. Later, besides the ‘WirelessMAN-SC’, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ were added to a physical layer in IEEE 802.16a standard approved in 2003. After the IEEE 802.16a standard was completed, a revised IEEE 802.16-2004 standard was approved in 2004. IEEE 802.16-2004/Cor1 was finalized in the form of ‘corrigendum’ in 2005 in order to resolve and correct bugs and errors of the IEEE 802.16-2004 standard.
Currently, the IEEE 802.16 broadband wireless access working group is conducting standardization of an IEEE 802.16m based on IEEE 802.16e. The IEEE 802.16m has evolved from the IEEE 802.16e.
Communication between a base station and a terminal is performed by a downlink (DL) transmission from the base station to the terminal and an uplink (UL) transmission from the terminal to the base station. The conventional IEEE 802.16e-based system profile supports a TDD (Time Division Duplex) scheme in which a downlink transmission and an uplink transmission are divided by time domains. The TDD scheme is a scheme in which an uplink transmission and a downlink transmission are performed during a different time period while using the same frequency band. The TDD scheme is advantageous in that frequency selective scheduling is simple because uplink channel characteristics and downlink channel characteristics are reciprocal. In IEEE 802.16m, an FDD (Frequency Division Duplex) scheme, as well as the TDD scheme, is considered. The FDD scheme is a scheme in which a downlink transmission and an uplink transmission are performed simultaneously through different frequency bands. In the IEEE 802.16e, a 5 ms frame of the TDD scheme is used, while in the IEEE 802.16m, an 20 ms superframe is considered to use both the TDD scheme and the FDD scheme.
In the IEEE 802.16e, when a mobile station (MS) has data to be transmitted to uplink, it performs a bandwidth request (BW REQ) procedure. The bandwidth request procedure in the IEEE 802.16e includes 4 steps: (1) transmitting a bandwidth request indicator; (2) transmitting a response message with respect to the bandwidth request indicator; (3) transmitting a bandwidth request message; (4) transmitting an uplink grant message; and (5) transmitting uplink data. One of predetermined orthogonal codes is selected as the bandwidth request indicator and transmitted through a contention-based channel. When the bandwidth request indicator transmitted by the MS does not collide with a bandwidth request indicator from a different MS, a base station (BS) transmits an uplink grant message for a bandwidth request message transmission in response to the bandwidth request indicator. Table 1 below shows an example of the uplink grant message for a bandwidth request message transmission.
TABLE 1SizeSyntax(bit)NotesCDMA_Allocation_IE0 {—— Duration6— UIUC4UIUC for transmission Repetition Coding20b00: No repetition coding Indication0b01: Repetition coding of 2 used0b10: Repetition coding of 4 used0b11: Repetition coding of 6 used Frame Number Index4LSBs of relevant frame number Ranging Code8— Ranging Symbol8— Ranging subchannel7— BW request mandatory11: Yes0: No}——
Upon receiving the uplink grant message, the MS transmits a bandwidth request message through determined radio resource. The bandwidth request includes information such as a connection identifier (CID) of the MS, the size of requested radio resource, and the like.
Upon receiving the bandwidth request message, the BS transmits an uplink grant message including information regarding the size and position of uplink radio resource for an uplink data transmission to the MS having the corresponding CID. Table 2 below shows an example of an uplink grant message for an uplink data transmission.
TABLE 2SyntaxSize (bit)NotesUL-MAP_IE0 {— CID16— Start Time11— Subchannel Index5— UIUC4— Duration10In OFDM symbols Midamble repetition interval20b00: Preamble only0b01: Interval 5: Midamble afterevery 4 data0b10: Interval 9: Midamble afterevery 8 data0b11: Interval 17: Midambleafter every 16 data symbols if(UIUC==4)—  Focused_Contention_IE( )16— if(UIUC==13)—  Subchannelized_Network_Entry_IE( )12— if(UIUC==15)—  UL_Extended_IE( )variableSee subclause Padding nibble, if needed4Completing to nearest byte, shallbe set to 0x0}——
The MS transmits uplink data through uplink radio resource indicated by the uplink grant message for an uplink data transmission. In transmitting the uplink data, a header including the CID of the MS and a CRC (cyclic redundancy check) for checking an error of data are added to the uplink data.
The IEEE 802.16m adopts various communication services such as an E-MBS (Enhanced Multicast Broadcast Service) for various multimedia services, a multi-hop relay for improving a service in a shadow area, a femto-cell for a high capacity service at homes or in offices. A macro-cell, a relay BS and a femto-cell may use different frequency bands in order to reduce interference. When numerous relay BSs or femto-cells are disposed in a macro-cell, inter-cell handover will be frequently performed, and accordingly, the MS will frequently perform a bandwidth request procedure. Besides, in continuously proving a high capacity real-time service like video communication, delay in the bandwidth request procedure may lead to a degradation of QoS (Quality of Service).
Thus, a method for effectively performing a bandwidth request procedure is required in order to improve QoS of a wireless communication system.